eglglessink: Make sure the buffer is released to the pool if it's the last used one
srtp: Add SRTP plugin based on libsrtp

In large part the work of Gabriel Millaire
audiovisualizer: fix improper video frame clear operation

The current code is memsetting the GstVideoFrame.data address to 0s (which
causes a segfault). This member is actually an array of data buffers (one for
each plane).  This fix iterates over each data plane to clear them all.

https://bugzilla.gnome.org/show_bug.cgi?id=695655
tests: fix up mpegtsmux unit test after collectpads change

It was passing expected flow returns (which might be negative)
in the buffer timestamp field, which was maybe not the best
idea.